A New and Efficient Synthesis of Coumestan and Coumestrol
摘要:
4-Aryloxy-3-iodocoumarins (4-aryloxy-3-iodo-2H-1-benzopyran-2-one), 4a-c, which are readily available by known procedures starting from 4-hydroxycoumarins 1a,b and diacetoxyiodobenzenes 2a-c; are cyclized with palladium chloride in triethylamine to yield the coumestanes (6H-benzofuran[3,2-c][1]benzopyran-6-ones) 5a-c.
A copper-catalyzed intramolecular cross dehydrogenative C–O coupling reaction of 2′-hydroxyl-3-arylcoumarins was developed. This protocol provided a facile and efficient strategy for the construction of natural coumestans and derivatives in moderate to high yields. This transformation exhibited good functional group compatibility and was amenable to substrates with free phenolic hydroxyl groups.